GNU/Linux offers a bewildering variety of flavors -- or distributions, as they're called. To a newcomer's eye, many of these seem virtually identical to each other.

Yet, the more you learn about a distribution and the community that surrounds it, the more different they become. Here, in alphabetical order, is a list of the seven distributions that have most affected GNU/Linux as a whole:

Debian

Named for founder Ian Murdock and his wife Debra, Debian may be the most influential GNU/Linux distribution yet. From Ubuntu, Knoppix, and MEPIS through to Xandros and Linspire, many of the best-known distributions today are based on Debian, and the percentage holds roughly true in any listing of distributions. Moreover, with over 1,000 developers and some 20,000 packages, as well as support for 11 different hardware architectures, Debian has a strong claim to being one of the largest free software projects in existence.

Debian is distinguished by its repository system. Each new package enters the unstable repository, then passes through testing to stable status as it meets quality assurance standards. Each of these repositories is further subdivided into three sections: Main,which contains only free software; contrib, which contains free software that requires non-free software to use, and non-free, which contains software not released under a free license. This system allows users to choose the high dependability of official releases, or to choose the balance between cutting edge software and dependability that they prefer. Similarly, the subdivisions allow users to choose the level of software freedom on their systems.

Debian has a reputation for being hard to install and use, neither of which is true today. The new Debian installer released a couple of years ago has taken the pain out of installation, while the prevailing ethos today seems to be to accommodate all levels of users from newbie to expert. Similarly, the frequent complaint that official releases are slow to emerge is largely irrelevant, since most users can get the latest software simply by installing from the appropriate repository.

What is true is that much of Debian's business is conducted publicly via mailing lists and votes, and with a minimum of politeness. This free-for-all is constantly luring outsiders to believe that Debian is about to fragment, yet somehow it never does. Still, the bluntness in the community can be intimidating at times.

Fedora and Red Hat Enterprise Linux (RHEL)

One of the oldest and most successful commercial distributions, these days, Red Hat is divided in two, with Fedora the community face and RHEL the corporate face. Although Red Hat is no longer as influential as in the days when its Red Hat Package Manager (RPM) was the norm, the two distributions remain among the most influential.

Fedora's main reputation is for being the first distro to include new innovations. For instance, Fedora was the first distribution to include tools that allowed average users to work with SELinux's detailed security options. In the same way, Fedora 7 was the first to include Smolt, a program for collecting hardware information about users; Revisor, a program for creating custom install disks, and the Liberation typefaces that provide the metrical equivalents of Arial, Helvetica, and Times Roman in free fonts. Although some users on Fedora mailing lists suggest that this innovation makes Fedora unsuitable for servers and mission-critical operations, an increased attention to testing is starting to make that generality obsolete. After a slow couple of years, Fedora is also well on the way to realizing its goal of creating a thriving community in which Red Hat is important, but no longer completely dominates decision-making.

For its part, RHEL remains one of the most successful commercial distributions. Since RHEL is released every 18-24 months, compared to Fedora's six-month schedule, it benefits from patches to Fedora to make a stable release. Much of RHEL's commercial success may be due to the Red Hat Certification Program, which is widely regarded as one of the most rigorous -- and, therefore, most desirable -- in the business.

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